He is a much-needed centre-back for the Lilies, who have seen Nicolai Rapp and Dario Dumić return to their parent clubs.
Mai has been with Bayern since 2014, joining them from Dynamo Dresden, but made only two first team appearances, both at the back end of the 2017-18 season.
He featured more regularly for the under-23 side and made 26 apperances for them last season as they marched to the 3. Liga title.
Speaking of a “talented player,” director of sport Carsten Wehlmann said that Mai had “showed that he has arrived in men’s football” last season and the club are “convinced that Lukas can take the next step in his development with us.”
Mai himself says he is “very happy” to get the chance to prove himself in the second tier. “I’m looking forward to the season in Darmstadt and I’m really looking forward to getting started with my new team,” he added.
The 20-year-old, who has been handed the number 17 shirt, is the brother of Sebastian Mai, formerly of Halle, who has just rejoined the brothers’ home town club of Dresden.
The confirmation of Mai’s arrival follows the club handing new contracts to two of its own youngsters, Ensar Arslan and Henry Crosthwaite, on Monday.